1. Field of the Invention
The present invention relates to an image processing, more particularly, to an image processing for overlaying an image on another image.
2. Description of Related Art
A technique of combining a plurality of images and displaying a composite image is widely used in an operating system (OS) of a personal computer (PC) or the like. Recently, some mobile terminal, embedded devices and so on have a function to create and display a composite image. A technique of efficiently creating and displaying a composite image is demanded since there is a limit to the memory size and processing speed in these devices.
To meet this demand, Japanese Unexamined Patent Publication No. 2003-87555 (Odakawa), for example, proposes a technique for producing a composite image from the two images by dividing each of the two images into a plurality of tile images and performing composition processing for each tile image. Since this technique divides the images, it is possible to perform image composition with a low processor load.
The approach disclosed in the above document divides the images individually into the tiled images of prescribed size, and then combine each pare of tiled images. It has now been discovered that, since a block size for composition processing is fixed to single tile size, it is difficult to perform composition process locating an overlay image on a pixel-to-pixel basis. Furthermore, image composition processing with image scaling is not examined in the above document.
A general method of creating a composite image with image scaling is to scale each image separately and combine the scaled images, or to scale one image and overlay another image thereon as scaling it. These methods, however, need to temporarily store each scaled image data and thus requires a large memory.